Getting the debt to GDP ratio to fall at some stage is a good idea, but having a target for a specific year is silly. It is not optimal because if some shock hits the economy before 2016/7 which means debt tends to rise relative to GDP, it is crazy to try and counteract that to meet the target in such a short space of time. It is not effective because it can be gamed by the government fiddling the timing of expenditures.

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Having a five year rolling target for the deficit allows fiscal policy plenty of time to adjust to shocks. We saw this in action over the last few years, as the Chancellor was able to reduce the pace of fiscal consolidation from 2012 when the economy failed to recover as quickly as he had hoped. Changing this mandate from five to three years gives any Chancellor less time to adjust, which is why it is a backward step.